Hi,

I keep fixing a leaking water neck gasket on my polara. It has a stock, tired, non-rebuilt 383. The problem is the flange where the thermostat goes in. It always leaks. I've fixed it a few times, and even bought a replacement new water neck. I clean the surfaces, use very light application of gasket sealer, and new gasket. I've done this several times. Funny thing is, it leaks even when I first start the car and the engine is barely warm.

I had a thought today. If the head gasket were allowing cylinder pressure to leak into the coolant, the water neck is where the leak would be seen, as the thermostat is closed. I haven't seen any traces of water in the oil, but the car does run hot even with a new radiator. Could a small head gasket leak be my issue?

Any bubbles in the rad. with eng. warmed up and running? The WP housing could be cracked or have a small sand hole.

Pull the water pump off and bolt on this tool. Then you add some air pressure (30 psi max) and you'll know right away if you have a leak somewhere.

Hughes Engines has the tool. Part number is AR282.

That's a good idea, can I do the same thing with one of those radiator cap pressure testor things?

are you sure it is not the hose?

seems unlikely it is the neck seal, since there are soo many other places that could blow out first.

if you left the cap off does it still leak?

I'll check to see if it leaks with the rad cap off. The thing is, it only leaks while it's running, which means either the pressure from the water pump (which is new) or pressure from somewhere else is causing it to leak.

again, why I think it might be the hose.

a small hole when presurized making the mess vs the neck itself leaking.

Well, I do know it's not the hose. I can see the coolant bubbling out from the connection between the water neck and the water pump housing. I thought it was the hose at first too, since that would be very easy to fix. But no, it's not.

If you had a small head gasket leak or cracked head, I would expect the radiator pressure cap to relieve the pressure before the water neck leaks. If you had a big gasket or crack problem, it would be spewing out gas/water/steam like crazy and be noticable.

I would have another look at the joint. That joint - as simple as it is - can be very sensitive. Any warpage or excessive torque on the two bolts can cause a leak. Die-cast chrome water necks (MP) are almost a guaranteed leak. I've learned this the hard way.

You are starting with an iron water neck which is good. They are not always true but they are stiff. I would use a straight edge on both the water pump housing and water neck. If there is any warpage, fix it. The last new iron water neck I bought came out of the box slightly warped. A belt sander works really well; a file would work OK also. I have used Permatex #1 - the hardening type - on problem water necks along with a new gasket. Install and torque gently. Too tight will warp it and cause a leak. Good luck!

Ahhh, I think I found one error. I know not to overtighten valve covers. But I have been cranking down on the water neck to fix the leak, which seems to only make it worse. I think I'll try removing it, using non-hardedning, and lightly torquing it upon reapplication. We'l see if that's the magic touch

The aluminum water necks (and chrome plated versions) are well known for leaks (cheap and mass produced = low quality). Take your aluminum neck and block sand the mating surface on a course grain sand paper. I have also done so on a flat, unpolished concrete surface, figure 8 pattern). You will quickly see how uneven the cast aluminum mating surface is. Once you have a 100% contact surface, you will have a good leak free seal with just a little bit of RTV and a new gasket.